Electrolytic refining of copper



ELECTROLYTIC REFINING OF COPPER Roland J. Lapee, Great Falls, Mont, assignor to The Anaconda Company, a corporation of Montana No Drawing. Application November 8, 1956 Serial No. 621,027

5 Claims. (Cl. 204-108) This'invention relates to the electrolytic refining of copper, and is particularly directed to the provision of an improved combination of addition agents in the electrolyte. The invention is based upon my discovery that when an acrylamide polymer hydrolyte is incorporated in the electrolyte in combination with an addition agent selected from the group consisting of glue and casein,-

a more satisfactory cathode deposit is formed than can be obtained using addition agents of the character and in the combination heretofore employed.

In the electrolytic refining of copper, an electric current is passed between cast'anodes of copper to be refined and cathodes of pure electrolytically refined copper, both the'anodes and cathodes being immersed in an electrolyte composed primarily of an aqueous solution of cupricsulfate acidified with sulfuric acid. Under the influence of the electric current, copper is dissolved from the anodes into the electrolyte, and is deposited from the electrolyte onto the cathodes in purified form. By adjusting the pH ofthe electrolyte as Well as the current density, the impurities present in the anode are not depositedat the cathode,'-but-'rather remain in solution in the electrolyte or accumulate in an insoluble anode mud.

Addition agents, 'which generally are complex organic compounds or mixtures of such compounds, are incorporatedin the electrolyte to insure the formation of a smooth and dense cathode deposit. Failure to use such an addition agent usually results in the development of substantial 'protuberance's, known as sprouts or trees, as the cathode deposit. Since the spacing between each anode and cathode in an electrolytic copper refining cell" is usually"'abo'ut 1% inches," it is easy for these sprouts "or trees, if they form, to'make contact with the neighborin'gtanode, thereby 'caus'ing a short circuit.- When-tnisoccurs,further'deposit' of'copper on the cathode is hindered'until the shortcircuit is broken, and both "cell voltage and overall cathode current density in"the' cell"'-'are' disturbed." Even if noshort"circuit"develops," the-formation 'ofa rough cathode deposit'is accomp'ani'ed by entrainment of pockets of electrolyte which cannot bewashed "out: Because the entrained electrolyte in :such 1 pockets contains, 'various impurities dissolved fromthe anode, the cathode' "copper is contaminated upon being melted. I

A great numberot additionagents' havebeen tested for use-in preventin'g'the "development'ofprojections on the cathode surface." Unfortunatelyfmany of these additio'niagents' ofteri'promote' undesirable properties, such as "hardness and brittleness in cathode deposits, and their use" generally" leaidsto reduced 'currentefficiencie's. Consequently', a sub'stantial amoun'tofwork has'been done tofin'd'an addition 'agent,'or'"combinatiomof addition agents, "thatgives a's' smooth" a 'depositas-possible with a minimum "of undesirable effects;

In""general,"the 'addition of a pro'tein'aceous 'electrophilic (positively i'charged) colloid to the electrolyte has been found-"effective topreVent'the' formation of sprouts or trees. The use of "'anin' a'bglumfin particular, has found Wide accepta'nCeQeither individually or-in combination with casein-tor Goulac- (a lignin pitch product obtained from paperdmill waste) 'or both. Manyre finer'iesi use,:.animal glue, incombination-with fGoula'c.

in electrolytic copper refining, but the major disadvantage of this combinationis that-the-- Gonlac tends to form insoluble carbonaceous compounds in the electrolyte which precipitate in the. tanks and the solution lines.

I have'discovered that acrylamide polymer hydrolytes', when incorporated inthe electrolyte in conjunction wlth one or more conventional addition agents, 'result'in -unusual advantagesin the refining of copper electrolytically.

in particular, when the'acrylamide polymer hydrolyte is used in combination with animal glue or casein, or both; the quality of the cathode deposit is superior in smoothness and freedomfrom-entrapped impurities, to thatobtained with any previouslyused addition agents or fcombination. In 'addition', the formation of harmful carbonaceous depositsis substantially avoided. Elimination of these carbonaceous depositsfwhichare characteristic of the. use of :Goulac;". in turn facilitates the"wa'shing," leaching; filtering. andsubsequent treatment of the ano'de slimes'for recovery oftheir metal values; i

Acrylamide polymer 'hydrolytes are"high'-molecu lar-" 3 weight polymers (and"*copolymers') of acrylamide in which from 0.8 'to" about 10 percent of car-boxamide' groups of the polymer are replaced by "carboxyl' groups-' These polym'er= hydrolyt'es, :which are marked by the Dow'Chemical Company under the trade name Separan, are characterizedbya viscosity of at least 4 centipolses asdetermined'withan Ostwald viscosi'mete'r for an 0.5 percent by weight aqueous solution' of thepolyme'r hydrolyte' at a pH of 3 to 3.5 and a temperature 'of"21.5

C. The termacrylamide polymer hydro1yte', however;'

methacrylon'itrile; vinyl "alk yl 'ethers, vinyl chloride, and vinylidene chloride.

The invention contemplates-the "improvement, in the: electrolytic refining of copper; of establishing and maintaining in theelectrolyte from' A to 5 ounces of an'addi-' tion agent' select'ed -trom the I group consisting of glue" and casein 'and se 1,; to 5 ounces"oflan' acrylamide'i polymer-*hydrolyte tor each' 'ton of copp'er deposited on" the: cathodes,the"=acrylamide polymer hydrolytehaving from about 0.8 to about 10 percent of the carboxamide groups vofthe polymerreplaced bycarboxyl groups, The

actual concentrations" of addition agents 'whichare most:

advantageous are',*l-;ot course, dependent upon several factors, including the current density, theimpu'rity con" tent of the'anodes; and the temperature and pH of the electrolyte. Although thereappearsto he no critical upper'limit to the concentrationof the" acrylarnide polymer hydrolyte, since this compound apparently functions 1 as a flocculant,there is nogreat a'dvantage'in using more than=about 2 ouncesper ton of copper deposited on the In most electrolytes, substantially the full benefit of thepres'ence- 'of' an acrylamide polymer hy drolyte may be achieved by' addin-g not morethan 1V2 ounces for each ton of copper deposited on the cathodes.

Thenacrylamidepolymer'hydrolyte appears to inne tion "best- When used in the electrolyte in combination" with animal glue orcasein. Surprisingly enough, casein' and-: glu'e produce hard, brittlecathode deposits when" either: is used alone as the 'addition agent, but when either-agent is combined'with theacryl'amide polymer hydrol-yteyrthe resultant cathode deposit is fine-grained) dense, and'-'.desirably:softL By adding to'the electrolyte cathodes.

animal-glue ill]. squantities as low as :"to 5 ounces to get-her with 1A to=5 ounces of the' acrylamidepolymer" hydrolyte per tonv'iofz'copperdeposited on=the cathode'sfi the surface of the deposit is smooth and completely free from any-objectionable trees or sprouts. In Similar results Patented May 25, 1959' 1 are obtained when A to 5 ounces of casein are substituted in the electrolyte for the animal glue.

To illustrate the improvements obtained in electrolytic refining of copper when an acrylamide polymer hydrolyte is added to the electrolyte in conjunction with animal glue, a preferred embodiment of the invention is described below:

A typical electrolytic copper refinery comprises a large number of electrolytic cells, each of which is in the form of a tank holding a considerable number of cast anodes of copper to be refined, arranged alternately with cathodes of pure electrolytically refined copper. The anodes and cathodes are hung vertically in the cell tank and are spaced apart by only a little over an inch. An electrolyte comprising an aqueous solution of cupric sulfate and sulfuric acid is introduced continuously into each cell tank at one end and is continuously withdrawn at the other. The electrolyte fills the tank almost to the tops of the anodes and cathodes. Although cupric sulfate and sulfuric acid are the main ingredients of the electrolyte solution, it generally also contains other substances, such as a small amount of sodium chloride, added to prevent antimony and bismuth impurities from accumulating in the solution, and soluble compounds of such anode impurities as arsenic, nickel and iron. The electrolyte flowing from the electrolytic cell passes through a circulation system including a sump where make-up amounts of required reagents (including the addition agents) are added; and a part of the electrolyte is continuously withdrawn for treatment to remove accumulations of arsenic, nickel and other impurities. The electrolyte is pumped back again from the sump to the electrolytic cell tank. It is most convenient to add the combination of addition agents contemplated by the invention to the electrolyte in the sump tank or well, the addition agents being added continuously in an amount calculated to maintain them in desired concentrations in the electrolyte.

Since both animal glue and the acrylamide polymer hydrolyte (e.g. Separan 2610) are quite readily soluble in water and in acid solution, the combination of addition agents is introduced in the electrolyte by preparing a. dilute solution which can be measured continuously into the circulating electrolyte. By suitably adjusting the ratio of the acrylamide polymer hydrolyte to animal glue 1n this addition solution, it is possible to introduce into the electrolyte from A to 2 ounces of the hydrolyte and from /4 to 5 ounces of the glue for each ton of cathode copper produced. Particularly satisfactory results have been obtained by adding glue in an amount from 1 to 2 ounces and Separan 2610 in an amount from /5 to 1% ounces for each ton of copper deposited on the cathodes.

If casein is to be used in the electrolyte in combination WIth bOth glue and Separan 2610, a separate dilute SOIUtIOH of casein may be prepared and run continuously in a measured amount into the electrolyte in the sump. The casein solution should be freshly prepared each day, since casein undergoes extensive decomposition if allowed to remam in contact with acid solution. When casein is used, however, the amount of glue added to the electrolyte may be correspondingly reduced.

The use of animal glue and Separan 2610 as additlon agents, in accordance with the invention, has resulted m a number of improvements in operating economy and efliciency. Not only is the current efliciency increased, when compared with the use of a glue-Goulac combination in the electrolyte, but the amount of organic deposits in the electrolyte is reduced. This in turn results in a more easily handled anode mud than is the case when other addition agents are used. Since both the glue and Separan 2610 are soluble in water and in acid solution, the addition agents may be easily and effectively disseminated in the electrolyte.

I claim:

1. In the electrolytic refining of copper, in which antil) odes of copper to be refined are electrolytically dissolved in an aqueous electrolyte of cupric sulfate and sulfuric acid and copper is deposited from the electrolyte on cathodes of pure copper, the improvement which comprises adding to the electrolyte from M1 to 5 ounces of an addition agent selected from the group consisting of glue and casein and from A to 5 ounces of an acrylamide polymer hydrolyte for each ton of copper deposited on the cathodes, said acrylamide polymer hydrolyte having from about 0.8 to about 10 percent of the carboxamide groups of the polymer replaced by carboxyl groups and being further characterized by a viscosity of at least 4 centipoises as determined for a 0.5 percent by Weight aqueous solution of the polymer hydrolyte.

2. In the electrolytic refining of copper, in which anodes of copper to be refined are electrolytically dissolved in an aqueous electrolyte of cupric sulfate and sulfuric acid and copper is deposited from the electrolyte on cathodes of pure copper, the improvement which comprises adding to the electrolyte from A to 2 ounces of glue, from to 2 ounces of casein, and from about to 2 ounces of an acrylamide polymer hydrolyte for each ton of copper deposited on the cathodes, said acrylamide polymer hydrolyte having from about 0.8 to about 10 percent of the carboxarnide groups of the polymer replaced by carboxyl groups and being further characterized by a viscosity of at least 4 centipoises as determined for a 0.5 percent by weight aqueous solution of the polymer hydrolyte.

3. In the electrolytic refining of copper, in which anodes of copper to be refined are electrolytically dissolved in an aqueous electrolyte of cupric sulfate and sulfuric acid and copper is deposited from the electrolyte on cathodes of pure copper, the improvement which comprises adding to the electrolyte from A to 5 ounces of glue and from to 2 ounces of an acrylamide polymer hydrolyte for each ton of copper deposited on the cathodes, said acrylamide polymer hydrolyte having from about 0.8 to about 10 percent of the carboxamide groups of the polymer replaced by carboxyl groups and being further characterized by a viscosity of at least 4 centipoises as determined for 0.5 percent by weight aqueous solution of the polymer hydrolyte.

4. In the electrolytic refining of copper, in which anodes of copper to be refined are electrolytically dissolved in an aqueous electrolyte of cupric sulfate and sulfuric acid and copper is deposited from the electrolyte on cathodes of pure copper, the improvement which comprises adding to the electrolyte from 1 to 2 ounces of glue and from /5 to 1% ounces of an acrylamide polymer hydrolyte for each ton of copper deposited on the cathodes, said acrylamide polymer hydrolyte having from about 0.8 to about 10 percent of the carboxamide groups of the polymer replaced by carboxyl groups and being further characterized by a viscosity of at least 4 centipoises as determined for a 0.5 percent by weight aqueous solution of the polymer hydrolyte.

5. In the electrolytic refining of copper, in which anodes of copper to be refined are electrolytically dissolved in an aqueous electrolyte of cupric sulfate and sulfuric acid and copper is deposited from the electrolyte on cathodes of pure copper, the improvement which comprises adding to the electrolyte from /4 to 5 ounces of casein and from A to 2 ounces of an acrylamide polymer hydrolyte for each ton of copper deposited on the cathodes, said acrylamide polymer hydrolyte having from about 0.8 to about 10 percent of the carboxamide groups of the polymer replaced by carboxyl groups and being further characterized by a viscosity of at least 4 centipoises as determined for a 0.5 percent by weight aqueous solution of the polymer hydrolyte. 

1. IN THE ELECTROLYTIC REFINING OF COPPER, IN WHICH ANODES OF COPPER TO BE REFINED ARE ELECTROLYTICALLY DISSOLVED IN AN AQUEOUS ELECTROLYTE OF CUPRIC SULFATE AND SULFURIC ACID AND COPPER IS DEPOSITED FROM THE ELECTROLYTE ON CATHODES OF PURE COPPER, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE ELECTROLYTE FROM 1/4 TO 5 OUNCES OF AN ADDITION AGENT SELECTED FROM THE GROUP CONSISTING OF GLUE AND CASEIN AND FROM 1/10 TO 5 OUNCES OF AN ACRYLAMIDE POLYMER HYDROLYTE FOR EACH TON OF COPPER DEPOSITED ON THE CATHODES, SAID ACRYLAMIDE POLYMER HYDROLYTE HAVING FROM ABOUT 0.8 TO ABOUT 10 PERCENT OF THE CARBOXAMIDE GROUPS OF THE POLYMER REPLACED BY CARBOXYL GROUPS AND BEING FURTHER CHARACTERIZED BY A VISCOSITY OF AT LEAST 4 CENTIPOISES AS DETERMINED FOR A 0.5 PERCENT BY WEIGHT AQUEOUS SOLUTION OF THE POLYMER HYDROLYTE. 